Wear-resistant alloys having complex microstructure

ABSTRACT

A wear-resistant alloy having a complex microstructure is provided. from the microstructure includes a range of about 19 to about 27 wt % of zinc (Zn), a range of about 3 to about 5 wt % of tin (Sn), a range of about 7.6 to about 11 wt % of silicon (Si), and a balance of aluminum (Al).

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2013-0051291 filed on May 7, 2013, the entire contents of which application are incorporated herein for all purposes by this reference.

TECHNICAL FIELD

The present invention relates to an aluminum alloy used for vehicle parts which may require wear resistance and self-lubricity, and a method of preparing the aluminum alloy. In particular, the present invention provides an aluminum alloy having a complex microstructure, which may include wear-resistant particles and self-lubricating soft particles.

BACKGROUND

As an aluminum alloy, a hypereutectic aluminum-iron (Al—Fe) alloy containing a range of about 13.5 to about 18 wt %, or about 12 wt %, of silicon (Si) and a range of about 2 to about 4 wt % of copper (Cu) has been generally used in a vehicle industry. Since such conventional Al—Fe alloy has a microstructure with primary silicon (Si) particles having a size of a range of about 30 to about 50 μm, it may have improved wear resistance compared to mere Al—Fe alloys, and thus it may be generally used for vehicle parts which may require wear resistance, such as a shift fork, rear cover, swash plate, and the like.

An example of commercial alloys may include: an R14 alloy (manufactured by Ryobi Corporation, Japan), a K14 alloy which is similar to the R14 alloy, an A390 alloy which is used for a monoblock or aluminum liner, and the like.

However, such hypereutectic alloys may have problems due to high silicon content, such as, low castability, low impact resistance, and the like. In addition, adjustment of size and distribution of silicon (Si) particles may be difficult, and manufacturing hypereutectic alloys may cost more than other aluminum alloys due to specifically developed process.

Meanwhile, an An-Sn alloy may be another example of self-lubricating aluminum alloy for vehicle parts. The An-Sn alloy may include a range of about 8 to about 15 wt % of tin (Sn), and further include microstructure of self-lubricating tin (Sn) soft particles, which may reduce friction. Therefore, such An-Sn alloy may be used as a base material of metal bearings used in high frictional contact interfaces. However, this An-Sn alloy may not be suitable for structural vehicle parts due to a substantially low strength of about 150 MPa or less, although the strength may be reinforced by silicon (Si) content.

The description provided above as a related art of the present invention is just merely for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.

SUMMARY OF THE INVENTION

The present invention may provide a technical solution to the above-mentioned problems. Therefore, in one aspect, the present invention provides a novel high-strength and wear-resistant alloy having a microstructure which may be obtained from both hard particles and soft particles thereof. In particular, the novel alloy may have both wear resistance from a hypereutectic Al—Si and self-lubricity from an Al—Sn alloy.

In one exemplary embodiment of the present invention provides a wear-resistant alloy having a complex microstructure, which may include: a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of tin (Sn); a range of about 7.6 to about 11 wt % of silicon (Si); and a balance of aluminum (Al). The wear-resistant alloy may further include from about 1 to about 3 wt % of copper (Cu). The wear-resistant alloy may also include from about 0.3 to about 0.8 wt % of magnesium (Mg). In addition, the wear-resistant alloy may include from about 1 to about 3 wt % of copper (Cu) and from about 0.3 to about 0.8 wt % of magnesium (Mg).

In another exemplary embodiment, the present invention provides a wear-resistant alloy having a complex microstructure, which may include: a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of bismuth (Bi); a range of about 7.6 to about 11 wt % of silicon (Si); and a balance of aluminum (Al).

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is an exemplary graph showing a correlation between friction efficient and tin (Sn) content in wt % or zinc (Zn) content in wt % of wear-resistant alloys having a complex microstructure according to an exemplary embodiment of Examples and Comparative Examples with respect to soft particles.

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about”.

Hereinafter, various exemplary embodiments of the present invention will be described in detail. The present invention relates to a novel alloy having a complex microstructure, which may include both hard particles and soft particles.

In certain examples of conventional aluminum alloys, alloy elements for forming self-lubricating particles may include tin (Sn), lead (Pb), bismuth (Bi), zinc (Zn) and the like. These alloy elements may not be formed into intermetallic compounds because they may not react with aluminum, and the phase thereof may be separated. Further, these alloy elements may have relatively low melting points, and have self-lubricity for forming a lubricating film while partially melting under a severe friction condition.

Among the above-mentioned four alloy elements, lead (Pb) may be is the most suitable element for forming self-lubricating particles when considering both self-lubricity and cost. However, lead is prohibited in a vehicle industry because it is classified as a harmful metal element. In this regard, tin (Sn) may be most widely used instead of Pb, and bismuth (Bi) may be used occasionally instead of Sn. In contrast, zinc (Zn) may be disadvantageous due to a substantially high melting point compared to Sn and Bi and substantially low self-lubricity. However, zinc may be in relatively substantial amount due to low cost. Therefore, in consideration of cost competitiveness, Zn may be used for forming soft particles, and partially replacing expensive Sn or Bi.

In addition, Si or Fe may be an alloy element for forming hard particles. Si or Fe may cause an eutectic reaction together with Al, and form angular hard particles when it is added in a predetermined amount or more. In an example of aluminum alloys, Si may be form hard particles, and form primary silicon particles. Further, Si may provide wear resistance when it is added to a binary Al—Si alloy in an amount of about 12.6 wt % or greater. However, when Si is added together with Zn which is an element for forming soft particles, Si content may be changed according to Zn content to form hard particles. For example, Si content may be about 7 wt % at minimum to about 14 wt % at maximum, when the Zn content is about 10 wt %. When the Si content is less than 7 wt % at minimum, hard particles may not be formed; and, when the Si content is greater than about 14 wt % at maximum, the size of hard particles may significantly increase, thereby creating a negative influence on mechanical properties and wear resistance.

In Al—Fe alloys, Fe may be an impurity. However, when an Al—Fe binary alloy contains no (e.g., minimal) Si and Fe is added in an amount of about 0.5 wt % or less, wear-resistant Al—Fe intermetallic compound particles may be formed, thereby providing wear resistance to the Al—Fe alloy. In contrast, when Fe is added in an amount of about 3 wt % or greater, the intermetallic compound particles may be excessively formed, thereby deteriorating mechanical properties and increasing the melting point.

Furthermore, alloy elements for reinforcing the strength of an exemplary aluminum alloy may include Cu and Mg. Cu may be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Cu with Al. The effect of Cu may vary depending on the Cu content, casting/cooling conditions or heat-treatment conditions. Mg may be effective in forming intermetallic compounds and increasing strength through a chemical reaction of Mg with Si or Zn. The effect of Mg may also vat depending on the Mg content, casting/cooling conditions or heat-treatment conditions.

Hereinafter, the present invention will be described in detailed exemplary embodiments.

In one exemplary embodiment, the aluminum alloy may include aluminum (Al) as a main component, and further includes a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of tin (Sn); a range of about 1 to about 3 wt % of copper (Cu); a range of about 0.3 to about 0.8 wt % of magnesium (Mg); and a range of about 7.6 to about 11 wt % of silicon (Si) for forming hard particles. When zinc (Zn), is added in an amount of less than about 19 wt %, a sufficient amount of Zn soft particles may not be formed, and thus it may be difficult to obtain sufficient self-lubricity. When zinc (Zn) is added in an amount of greater than about 27 wt %, the solidius line of the aluminum alloy may become substantially low, and thereby deteriorating casting conditions.

Further, tin (Sn) may have greater self-lubricity than zinc (Zn). When tin (Sn) is added in an amount of less than about 3 wt %, a sufficient amount of Sn soft particles may not be formed, and thus it may be difficult to compensate for insufficient self-lubricity of Zn soft particles. When tin (Sn) is added in an amount of greater than about 5 wt %, the friction reducing effect of the aluminum alloy may not be obtained under a driving condition, the thus amount of Sn may be minimized in terms of efficiency.

Silicon (Si) may form hard particles. When silicon (Si) is added in an amount of less than about 7.6 wt %, primary Si hard particles may not be formed sufficiently, for instance, less than about 0.5 wt %, and it may be difficult to ensure wear resistance. When silicon (Si) is added in an amount of greater than about 11 wt %, the primary Si hard particles may be excessively formed, for instance, greater than about 5 wt %, thereby coarsening hard particles and creating a negative influence on wear resistance and mechanical properties.

Copper (Cu) may improve mechanical properties, and copper (Cu) may be added in an amount of about 1 wt % or greater to ensure sufficient mechanical properties. However, when copper (Cu) is added in an amount of greater than about 3 wt %, other elements and intermetallic compounds may be formed to deteriorate the mechanical properties of the aluminum alloy, and thus the amount of copper (Cu) may be limited. Alternatively, magnesium (Mg), instead of Copper (Cu), may be added in an amount of about 0.3 wt % or greater, and the mechanical properties of the aluminum alloy may be additionally improved. However, when magnesium (Mg) is added in an amount of about 0.8 wt % or greater, compounds deteriorating the mechanical properties of the aluminum alloy may be formed, and thus the amount of magnesium (Mg) may be limited.

The low frictional characteristics of the Al—Zn—Sn alloy according to an exemplary embodiment of the present invention have been evaluated with respect to soft particles. As shown in FIG. 1, exemplary alloys of Examples and Comparative Examples were prepared while changing the amount of Zn and Sn, and then the changes in friction coefficients of the alloys were measured. As a result, under a condition of about 3 wt % Sn, exemplary 3Sn-19Zn alloys of Examples may obtain desired low frictional characteristics, for instance, friction coefficient of about 0.150 or less, and exemplary 3Sn-17Zn alloys of Comparative Examples may obtain undesired results. Therefore, when Zn is added in an amount of about 19 wt % or greater based on about 3 wt % or greater of Sn, desired low frictional characteristics may be obtained. In addition, when the amounts of Sn and Zn increases, satisfactory low frictional characteristics may be obtained. The results of evaluation of wear resistance and mechanical properties of exemplary Al-25Zn-3Sn-xSi alloys of Examples and Comparative Examples are given in Table 1 below.

TABLE 1 Zn Sn Si Cu Mg Si particle Strength Class. Al (wt %) (wt %) (wt %) (wt %) (wt %) fraction (%) (MPa) Comp. residue 25 4 7 2 0.5 0 — Examples residue 25 4 7.4 2 0.5 0.3 — Examples residue 25 4 7.6 2 0.5 0.5 335 residue 25 4 8.4 2 0.5 2 — residue 25 4 11 2 0.5 5 345 Comp. residue 25 4 11.2 2 0.5 5.2 — Example

In Table 1 above, when exemplary Al-25Zn-3Sn-xSi alloys of Comparative Examples which may include a range of about 7.6 to about 11 wt % of Si, Si hard particles may be formed in a maximum amount of about 5 wt %, thereby obtaining sufficient wear resistance. In contrast, when Si is included in an amount of about 11.2 wt %, primary Si particles may be formed in an amount of greater than about 5 wt %, and Si particles may be coarsened and segregated, and thus the amount thereof may be limited.

Meanwhile, the strengths of exemplary Al-25Zn-35Sn-xSi alloys may be a range of about 335 to about 345 MPa regardless of the amount of Si, and thus these alloys may be used as structural materials for vehicle parts. The aluminum alloy according to another exemplary embodiment of the present invention may include: a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of bismuth (Bi); a range of about 7.6 to about 11 wt % of silicon (Si); and a balance of aluminum (Al). In particular, bismuth (Bi) may be used as a strong self-lubricating material instead of tin (Sn).

As described above, the wear-resistant alloy having a complex microstructure according to exemplary embodiments of the present invention may have both the wear resistance from a hypereutectic Al—Si alloy and the self-lubricity from an Al—Sn alloy, thereby achieving high strength and excellent wear resistance.

Although the exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

What is claimed is:
 1. A wear-resistant alloy having a complex microstructure, comprising: a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of tin (Sn); a range of about 7.6 to about 11 wt % of silicon (Si); and a balance of aluminum (Al).
 2. The wear-resistant alloy of claim 1, further comprising: a range of about 1 to about 3 wt % of copper (Cu).
 3. The wear-resistant alloy of claim 1, further comprising: a range of about 0.3 to about 0.8 wt % of magnesium (Mg).
 4. The wear-resistant alloy of claim 1, further comprising: a range of about 1 to about 3 wt % of copper (Cu) and from about 0.3 to about 0.8 wt % of magnesium (Mg).
 5. A wear-resistant alloy having a complex microstructure, comprising: a range of about 19 to about 27 wt % of zinc (Zn); a range of about 3 to about 5 wt % of bismuth (Bi); a range of about 7.6 to about 11 wt % of silicon (Si); and a balance of aluminum (Al). 